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Fasting for 24 Hours Has Bad Consequences |
Fasting was once considered an effective way to prevent or treat chronic diseases such as cancer, obesity and heart disease. But a study in mice suggests that prolonged fasting may impair the immune system. Related research was published in “Immunity” on February 23.
Fasting all day can damage the immune system. Image credit: SewCream/Shutterstock
Researchers including Filip Swirski of the Icahn School of Medicine at Mount Sinai in New York, USA, analyzed blood and tissue samples from five mice that hadn’t eaten for 24 hours, and compared these blood test results with those of mice that ate a normal diet. The results showed that the average number of monocytes, a type of white blood cell that helps fight infection and heal damage, was less than 10 percent in fasted mice.
“These cells are key to the immune system,” Swirski said. The researchers found that this decrease was due to the withdrawal of monocytes from the blood to the bone marrow, where they largely lay dormant.
When the fasted mice were fed again, the monocytes quickly returned to the bloodstream. Because there are excess monocytes dormant and they survive longer than normal in the bone marrow, these mice exploded when re-fed, Swirski said. These mice had an average 4-fold increase in the number of monocytes in their blood compared to mice that were either continuously fasted or never fasted.
To see how this affects immunity, Swirski’s team injected 45 mice with a bacterium that infects the lungs. Twenty-three of the mice were fasted for 24 hours before the injection, and the researchers then allowed them access to food.
After 72 hours, nearly 90 percent of the fasted mice died, compared with about 60 percent of the never-fasted mice. In addition, the diet-restricted mice had higher levels of inflammation, suggesting that prolonged fasting impairs the immune response.
However, the most common fasting regimens in humans don’t last 24 hours, says Satchidananda Panda of the Salk Institute for Biological Studies in California. His own research showed that fasting for 15 hours actually boosted immunity in mice.
Swirski said these findings are important for how we choose the duration of fasting and consider its impact. “Like many things in life, balance is important. What may be beneficial on one side may have unintended negative effects on the other,” he said.
Related paper information: https://doi.org/10.1016/j.immuni.2023.01.024